Hi all, sorry for posting another thread on a topic that is currently in discussion, but I would like to do it differently.

I would like to build a gunfire sound generator that works on propane.

The generator would be used for Airsoft Milsim to increase immersion. However, in a sport where you point replica firearms at each other; adding a combustion cannon onto the end means that, above all, it needs to be safe.

So why is this any different to all of the other topics? I have two things that I need to do very differently to them;

1- While replicating the gunshot of an AR-15 would be great for milsim, when not at a mislim event (i.e. a standard skirmish / test firing) I would like to avoid irritating my neighbours or give anyone standing next to me tinnitus. Therefore I am aiming for it to sound like an .223 AR-15 shot, just around the volume of a .22 rifle or similar. (This should also mean that it is more efficent than if I was replicating an AR-15).

2- This is required to fit completely into a rifle (with a line to a very small backpack for resovoirs and solenoids) but I do not have enough space to mount something the size of the BL Tech BOSS unit (grenade launcher) so I am aiming for this: the actual cannon should be the size of a sure fire scout light (e.g M600V) https://instagram.com/p/zvuiNLBIyW/ and the propane resovoir and solenoids into a small backpack (bearing in mind this is next to a 48ci HPA tank for the gun itself, which can also be used to supply air to the unit).

So the basic idea is:

Somehow create a combustion chamber the size of that torch, install a DIY medium pressure actuated valve on the end, so that at rest it can hold a little bit of pressure and still be airtight. I have the trigger hooked up to a raspberry pi zero, and three outputs from it. When I press the trigger it will spark the spark plugs (the first shot does nothing) then after a very, very small delay, release propane and air into the chamber from the resovoir and tank using the solenoid valves. On the second (and any shots after this) the trigger will spark the spark plug, triggering the propane air mix added from the previous shot to detonate and the pressure actuated valve will open, releasing a large bang. I have done it in this 'pre-loading' way so that it can shoot as fast as possible.

Any ideas how i could go about this? Any constructive criticism or ideas are greatly appreciated!